How To View Undelivered Emails Sendmail

the command is

# mailq

mailq - print the mail queue

SYNOPSIS
mailq [-Ac] [-q...] [-v]

DESCRIPTION
Mailq prints a summary of the mail messages queued for future delivery.

The first line printed for each message shows the internal identifier used on this host for the message with a possible status character, the size of the message in bytes, the date and time the message was accepted into the queue, and the envelope sender of the message. The second line shows the error message that caused this message to be retained in the queue; it will not be present if the message is being processed for the first time. The status characters are either * to indicate the job is being processed; X to indicate that the load is too high to process the job; and - to indicate that the job is too young to process. The following lines show message recipients, one per line.

hi there... i was told an email address was closed so i would not be able to send an email to that address. i sent a test email to see if the recipient would get it and it did not come back. does it always come back "not delivered" if it isn’t delivered or would it just get lost in email space? or is that person just saying their account is closed. thank you!